We are studying the altered growth regulation of cancer cells, emphasizing tumor virology, cell differentiation, and cell surface immunology and biochemistry. We will characterize the genome structure and transforming proteins of a variety of DNA and RNA tumor viruses. We will investigate the control of gene expression in cells expressing specific gene products, emphasizing transcription, processing and translation of messenger RNA. We will study aspects of normal rat mammary gland differentiation, and properties of tumor cell lines derived from mammary tissue. We will characterize cell surface glycoproteins, receptors and antigens on normal and malignant cells.